PLC faulty

Hi everybody,

I have a SLC-03 which faults once in a while.I have to download the program each time this happens.Today when I try to go online I god error 15.Looked it up "INvalid name stored in the SLC500-must download the program".
I grounded the chasis with a higher gage (12) but still same issuem.
I am going to install an eeprom if this happens again.
any ideas ?

Thanks

I have had similar problems with other brands of plc's. In some factories there were a lot of voltage spikes from machines and other equipment. 120vac solenoids can be a big problem, along with some larger contactors. We have installed AC line filters for plc's in the cabinet, and suppressors on solenoids, contactors, and relays. Can't gaurentee that this works everytime and with every plc, but it did the job for us at a couple of jobsites.

I will note that the factories were near each other and on the same primary utility circuit. The utility company substation was within a mile, and that may have induced some strange spikes into the powerlines when switching, too.

While a very remote possibility, that utility, (and many others) send data on the powerlines to control substation equipment, and I've often wondered what, if any, interference it would cuase with other stuff. With internet, cable television, telephone, and who knows what else, there is potential for wierd stuff to happen. I can't say that it will, or won't.


regards....casey

To further elaborate upon what kc9ih has wrote:

I have had similar problems in the past (epecially with our Mexico projects) due to the quality of power abroad and in one case in particular a project here in CA that was 150 yards from a power substation.

We have now made it manditory to install power conditioners (Isatrol, for example) to every control cabinet that we fab. This has solved a majority of the "spike" and poor power issues that we had encountered from in the past. This of course is not a solve-all cure but certainly power conditioning is a big plus. Other helpful components to your power would be isolation transformers, suppression where necessary, etc.

Regards,
Chris

thank you,
what type of suppressors did you use ?
were they installed on each output terminals?
We have installed those 120v power conditioners for the plc input.

When I use GE Fanuc PLC's, I use their supressors on the output, it is a MOV (metal ovide varistor), and any generic one should work. Most larger manufacturers should have them. For other brands of plc's, I make a plug in unit in a relay housing with generic mov's from Allied Radio or Newark Electronics. I use gas discharge units for phone or land lines.

regards.....casey

These are all good suggestions posted here. These considerations should already be consided in a well designed system. However the reality is that there is someting wrong with the CPU or Power supply on the PLC. My guess is the CPU. I doubt that a spike would knock out the memory without damaging it or some other component necessary for operation of the CPU. I would replace the cpu.

Actually Mike, I would normally agree with you (and normally this is the culprit) but I have seen first hand, power spikes "wipe" the memory of a perfectly good working processor.

This has happened to me before, once again, in locations that have unclean and/or "spike" problems. So before throwing out that processor or power supply, I would check the incoming power of a system.

Regards,
Chris

I am not sure if I have ever stumbled across a bad CPU or not. But then, the majority of stuph I see is new, or used pieces hacked together going into service, or being yanked out of service. The initial two PLC2's I place in service in '88 were still running fine in 99 when I was there last. I had 300 Fanucs in operation and another 100 or so other brands at the tire plant, with no failures the year I was there, except for two systems.

Sixnet pc board type units - we had an old retured out of balance machine for hummer tires, with two sixnet boards and no documentation. Replaced both boards (about $1900 each) , downloaded the program, and no change. Swapped boards back and forth for weeks, One day the stupid thing started working, with the two original boards in it. Never figured out why.

Had a couple hundred PID inputs into to OPTO22 units of some kind. Had to go into the pits below the tire presses every 10 days or so and reload the programs. Never did figure that one out, either.

It would have been more cost effective for me to put in 9030's then waste all that time. But, the way budgets are wrote, I could put a micro PLC in for a timer or doorbell circuit, but couldn't replace the pristine looking opto22.

enough rambling........casey

Consequently, I avoid Sixnet and OPTO22 units. I do like opto's isolators, though.

Chris,

The reason for my argument as the CPU (or some faulty component of the CPU module) as being the culpret is due to the usual hardware arcutecture of the PLC, and the usual high degree of isolation of the memory from the incoming power supply. If there is a power supply problem that is dramatic enough to change some of the memory, (any memory area), it would have likely cause other permament damage.

Contrary to popular belief, solid state components, such as memory, ttl logic devices, etc. do actually wear out. Over the years, as breakdown occurs funny things start to happen. If dirty power is causing memory problems, fix the power supply and change out the CPU. Dont spend thousadns of $$$ in service calls and trouble shooting trying to convince yourself that you dont have to change out a $200.00 CPU. Just do it so you can go on to the next project.

I've had three CPUs with the same issue here, GE series 3, DL230, and a GE 90-30. No known reason. It just happens. I dont waste my time anymore.

Mike.